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    <title>向量</title>
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    <div>向量(Vector)是描述偏离空间某点的方向及长度的量。一般用加粗字母<b>a</b>表示。</div>
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        <div>当两个向量的长度与方向一致时，则认为这两个向量相等。即使它们处于空间的不同位置(因为向量不是描述位置的量)。</div>
        <svg version="1.1" width="128" height="86" xmlns="http://www.w3.org/2000/svg">
            <rect x="0" y="0" width="128" height="86" stroke="black" fill="none" />

            <line x1="16" x2="96" y1="32" y2="16" stroke="black" />
            <line x1="96" x2="90" y1="16" y2="12" stroke="black" />
            <line x1="96" x2="92" y1="16" y2="22" stroke="black" />

            <line x1="16" x2="96" y1="68" y2="52" stroke="black" />
            <line x1="96" x2="90" y1="52" y2="50" stroke="black" />
            <line x1="96" x2="92" y1="52" y2="56" stroke="black" />
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    <div>向量运算</div>
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        <div>向量加法：两个向量首尾相连后，其新的首位构成新的向量</div>
        <svg version="1.1" width="128" height="86" xmlns="http://www.w3.org/2000/svg">
            <rect x="0" y="0" width="128" height="86" stroke="black" fill="none" />
            <text x="16" y="60" transform="rotate(-32)">a+b</text>
            <line x1="16" x2="96" y1="68" y2="16" stroke="black" />
            <line x1="96" x2="90" y1="16" y2="12" stroke="black" />
            <line x1="96" x2="92" y1="16" y2="22" stroke="black" />

            <text x="38" y="75">a</text>
            <line x1="16" x2="64" y1="68" y2="58" stroke="black" />
            <line x1="64" x2="60" y1="58" y2="54" stroke="black" />
            <line x1="64" x2="62" y1="58" y2="64" stroke="black" />

            <text x="82" y="48">b</text>
            <line x1="64" x2="96" y1="58" y2="16" stroke="black" />
            <line x1="96" x2="94" y1="16" y2="14" stroke="black" />
            <line x1="96" x2="94" y1="16" y2="18" stroke="black" />
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        <div>向量减法：两个向量起点相连后，从长度较短向量的终点指向较长向量的终点的新向量</div>
        <svg version="1.1" width="128" height="86" xmlns="http://www.w3.org/2000/svg">
            <rect x="0" y="0" width="128" height="86" stroke="black" fill="none" />
            <text x="16" y="60" transform="rotate(-32)">b</text>
            <line x1="16" x2="96" y1="68" y2="16" stroke="black" />
            <line x1="96" x2="90" y1="16" y2="12" stroke="black" />
            <line x1="96" x2="92" y1="16" y2="22" stroke="black" />

            <text x="38" y="75">a</text>
            <line x1="16" x2="64" y1="68" y2="58" stroke="black" />
            <line x1="64" x2="60" y1="58" y2="54" stroke="black" />
            <line x1="64" x2="62" y1="58" y2="64" stroke="black" />

            <text x="82" y="48">b-a</text>
            <line x1="64" x2="96" y1="58" y2="16" stroke="black" />
            <line x1="96" x2="94" y1="16" y2="14" stroke="black" />
            <line x1="96" x2="94" y1="16" y2="18" stroke="black" />
        </svg>
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